FIG. 1 shows the structure of a work equipment 2 provided in the front portion of a vehicle body 1a of a wheel loader 1.
As shown in FIG. 1, the work equipment 2 is constituted by a boom 3 and a bucket 4. The base of the boom 3 is attached to the vehicle body 1a so that the boom can be rotated up and down, and the bucket 4 is attached to the distal end of the boom 3 so as to be rotatable in the dump direction and tilt direction.
A rod 5a of the boom hydraulic cylinder 5 is attached to the boom 3, and a body 5b of the boom hydraulic cylinder 5 is attached to the vehicle body 1a. Where the rod 5a of the boom hydraulic cylinder 5 is extended, the boom 3 is actuated up, and where the rod 5a of the boom hydraulic cylinder 5 is contracted, the boom 3 is actuated down.
A bell crank 7 is swingably attached to the boom 3. A rod 6a of a bucket hydraulic cylinder 6 is attached to one side in the longitudinal direction of the bell crank 7. A body 6b of the bucket hydraulic cylinder 6 is attached to the vehicle body 1a. One end of a rod 8 is attached to the other end in the longitudinal direction of the bell crank 7, and the other end of the rod 8 is attached to the bucket 4. Where the rod 6a of the bucket hydraulic cylinder 6 is extended, the bucket 4 is actuated in the tilt direction, and where the rod 6a of the bucket hydraulic cylinder 6 is contracted, the bucket 4 is actuated in the dump direction.
The boom 3 rotates about a rotary shaft 3a located at the base thereof, and a boom angle sensor 9 that detects a rotation angle θ (referred to hereinbelow as boom angle θ) of the boom 3 is provided at the rotary shaft 3a. 
The bucket 4 rotates following the swinging of the bell crank 7, and a bell crank angle sensor 10 that detects a swinging angle φ (referred to hereinbelow as bell crank angle φ) of the bell crank 7 is provided at a swinging shaft 7a of the bell crank 7.
A stroke L of the bucket hydraulic cylinder 6 can be uniquely calculated on the basis of the boom angle θ, bell crank angle φ, and well-known data relating to the link mechanism including the bell crank 7 and the rod 8.
The boom 3 is actuated by operating a boom operation lever 11 provided in an control cabin. The bucket 4 is actuated by operating a bucket operation lever 12 provided in the control cabin.
Patent Document 1 indicated hereinbelow describes the invention relating to a hydraulic shovel equipped with a work equipment having a structure in which the body of a boom hydraulic cylinder is attached to a vehicle body, the body of an arm hydraulic cylinder is attached to the boom, and a bucket hydraulic cylinder is attached to an arm. In this hydraulic shovel, a pressure oil is supplied by small amounts via a throttle to the hydraulic cylinder when the work equipment is actuated in order to restrict the abrupt outflow of the pressure oil maintained between the hydraulic cylinder and the flow rate directional control valve and moderate the impact acting upon the vehicle body when the work equipment is stopped.
Patent Document 1: Japanese Patent Application Laid-open No. 2002-54609.